1. Field of the Invention
The present invention relates to a linear light source device, and more particularly to a linear light source device with SMD (surface mounting device) type light emitting elements.
2. Description of the Prior Art
The conventional image-capturing device, such as scanner, utilizes a light source device to provide a light source for illuminating an original upon performing a scanning action. A photoelectric detecting device detects the light penetrating or reflected from the original, and then transmitting to a personal computer to process the captured image information. In general, the light source device needs to provide a linear light source with steady light intensity. The intensity difference of each portion of the luminance area of the linear light source is required as small as possible to ensure the brightness of the captured image exact, not distorted. Especially for capturing a colorful image, the light source device needs to provide a white linear light source with steady light intensity in order that the brightness and color of the captured image and recovery of the original can attain high quality.
The light source utilized in the conventional image-capturing device includes cold cathode fluorescent lamp (CCFL) and light emitting diodes in a linear array. Referring to FIG. 1A and FIG. 1B, since the cold cathode fluorescent lamp 10 illuminates light 16 in all direction, a semi-cylindrical reflector 12 is used for concentrating the light 14 emitting from the cold cathode fluorescent lamp 10 and then illuminating upon the original. Moreover, before a scanning action begins, it is necessary to warm up the cold cathode fluorescent lamp 10 until the illumination of the cold cathode fluorescent lamp 10 attains steady state. The life time of the cold cathode fluorescent lamp 10 is about ten thousand hours, causing the limitation of the time of usage. The cold cathode fluorescent lamp 10 also has a low efficiency of. illumination and large heat dissipation during illumination. The power is largely consumed. Thus, there are many drawbacks for using the cold cathode fluorescent lamp 10 as the light source.
The life time of the light emitting diode device is about one hundred thousand hours. The light source of the light emitting diode device can be used at once upon the image-capturing device is powered on. Thus, it is more convenient for using the light emitting diode device than the cold cathode fluorescent lamp 10. FIG. 2A to FIG. 2C show a conventional light source device 20 formed of SMD type light emitting diodes 22 arranged in a linear array parallel to the photo-sensor array of the image-capturing device. The conventional light source device 20 includes a print circuit board 21 having a plurality of recesses 23 formed of truncated circular cones in a linear arrangement thereon. Each of the recesses 23 has a flat bottom 24 for placing the light emitting diode 22. A transparent plastic sealing 25 is filled in the recess 23 to cover the light emitting diode 22. Referring to FIG. 2B, the light emitting diode 22 provides a circular illumination area outward from the print circuit board 21 due to the package thereof. When the light source device 20 is used as the linear light source of the image-capturing device, the illumination from the light emitting diode 22 along the transverse direction of the print circuit board 21 would be wasted. Therefore, it is necessary to place more light emitting diodes 22 on the print circuit board 21 so as to attain the required illumination. The manufacturing of the light source device 20 can not be cost down. The power supplied for the light emitting diodes 22 is also increased.
FIG. 3A to FIG. 3C show another conventional light source device 30 formed of SMD type light emitting diodes 32 arranged in a linear array parallel to the photo-sensor array of the image-capturing device. The conventional light source device 30 includes a print circuit board 31 having a plurality of recesses 33 formed of truncated square cones in a linear arrangement thereon. Each of the recesses 33 has a flat bottom 34 for placing the light emitting diode 22. A transparent plastic sealing 35 is filled in the recess 33 to cover the light emitting diode 32. Referring to FIG. 3B, the light emitting diode 32 provides a square illumination area outward from the print circuit board 31 due to the package thereof. When the light source device 30 is used as the linear light source of the image-capturing device, the illumination from the light emitting diode 32 along the transverse direction of the print circuit board 31 would be wasted. Therefore, the light source device 30 confronts the same problems mentioned above.
Accordingly, it is an intention to provide a light source device with SMD type light emitting elements, which can overcome the above drawbacks by changing the package thereof.